KR20030091590A - Time Domain Synchronous-Orthogonal Frequency Division Multiplexing transmitter and a method processing OFDM signal thereof - Google Patents

Abstract

PURPOSE: A TDS-OFDM(Time Domain Synchronous-Orthogonal Frequency Division Multiple) transmitter and a method for processing signals in the same are provided to reduce the distortion of data conveyed by a sub-carrier by reducing an interval between sub-carriers as a certain frequency in a frequency domain and reducing signal distortion generated in a both end band of an SRRC(Square Root Raised Cosine) filter. CONSTITUTION: An 3780-IDFT(Inverse Discrete Fourier Transform)(300) processes signals so that a frequency interval(D) is X/N. The X is a bandwidth occupied by N sub-carriers. The 3780-IDFT(300) performs the inverse Fourier transform of a time domain as N sample data. A GI(Guide Interval) inserting unit(500) inserts a GI into the N sample data. A PN(Pseudo Noise) unit(600) inserts a PN sequence into the N sample data into which the GI is inserted. A 0.11 SRRC filter unit(700) filters the waveform of an OFDM signal having the PN sequence, the GI and the N sample data according to a certain roll off coefficient(r). The 3780-IDFT(300) processes the signals so that the frequency interval(D) is less than 2KHz. The roll off coefficient(r) is greater than 0.05.

Description

Time domain synchronous-orthogonal frequency division multiplexing transmitter and a method processing OFDM signal

The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) transmitter, and more particularly to a TDS (Time Domain Synchronous) -OFDM transmitter.

Orthogonal Frequency Division Multiple (OFDM) technology is commonly used for digital audio broadcasting (DAB), digital television, wireless local area network (WLAN) and wireless asynchronous transmission. It is widely applied to digital transmission technologies such as wireless asynchronous transfer mode (WATM). The OFDM scheme is a multi-carrier technology in which data to be transmitted is divided into several pieces, modulated, and then transmitted in parallel. The OFDM scheme is similar to the conventional FDM, but most of all, the optimal transmission efficiency is obtained in high-speed data transmission by maintaining orthogonality between subcarriers.

1 is a schematic block diagram of a conventional TDS-OFDM transmitter.

The input data bit stream is coded so that a receiver (not shown) can detect and correct an error by an error detection method set by the FEC 10. Thereafter, the input data is serial data input by the serial / parallel conversion unit 20 is converted into 3780 parallel data and output. Here, 3780 represents the index of the frequency domain and the subcarrier, and 3780 parallel data are defined as one OFDM symbol in the frequency domain. Subsequently, the 3780-IDFT, i.e., the 3780 point Inverse Discrete Fourier Transform (IDFT) unit 30, converts 3780 parallel data into 3780 subcarriers whose frequency spacing D is 2KHz. Perform Inverse Fourier Transform.

As shown in FIG. 2, at this time, as the interval D between subcarriers becomes 2KHz, a band occupied by one OFDM symbol data becomes 7.56MHz (3780 × 2KHz = 7.56MHz). Meanwhile, the available band becomes 0.44 MHz for a typical 8 MHz bandwidth, and available bands are provided by 0.22 MHz in both bands of 7.56 MHz.

This OFDM symbol data is modulated using the 3780-IDFT 30 to be output in the time domain signal, which is 3780 pieces of sampling data having a sampling rate of 7.56 MHz.

The 3780 sample data output in parallel from the 3780-IDFT 30 are converted into serial data by the parallel / serial conversion unit 40 and outputted. The GI (Guard interval) inserting unit 50 outputs the serial data output. A guard interval (GI) is inserted and output in 3780 sample data units, that is, in one OFDM symbol unit. The guard interval is a data obtained by copying some sample data at the end of the OFDM symbol composed of 3780 sample data and is inserted at the front of the OFDM symbol. Thereafter, the PN unit 60 inserts a timing synchronization signal and a PN sequence for channel prediction in front of the guard period GI in the signal in which the guard period is inserted.

A 0.05 square root raised cosine (SRRC) filter unit 70 is provided to shape the PN sequence into a predetermined waveform with respect to the generated signal, and the OFMD frame into which the PN sequence is inserted is provided by the 0.05 SRRC filter unit 70. After filtering, the OFDM signal is transmitted to the wireless channel through the RF unit 80.

As in the TDS-OFDM transmitter described above, the sampling rate of sample data in the time domain that is modulated and output using the 3780-IDFT 30 is 7.56 MHz.

In general, when 3780 parallel data are composed of one OFDM symbol, the rolloff coefficient r of the 0.05 SRRC filter unit 70 is defined according to the characteristic that the bandwidth of the subcarrier occupying in the frequency domain should not exceed 8 MHz. That is, as the conventional 3780 subcarriers are arranged at a frequency interval D of 2 KHz in the frequency domain, the band occupied by the subcarriers becomes 7.56 MHz. In other words, when the bandwidth occupied by the subcarrier is 7.56 MHz, the rolloff coefficient r of the 0.05 SRRC filter unit 70 is 0.05.

This result is obtained by the following procedure. When the 0.05 SRRC filter unit 70 having a rolloff coefficient r of 0.05 is used, the overall bandwidth is 7.56 + 0.378 = 7.938 MHz, which is 7.56 MHz × 0.05 = 0.378 MHz, so that the general bandwidth of 8 MHz is not exceeded. The rolloff coefficient r of the SRRC filter unit 70 cannot be larger than 0.05.

As described above, the smaller the rolloff coefficient r is, the more inclined the both ends of the 0.05 SRRC filter unit 70 become, so that the OFDM symbol passing through this region has distortion. In order to reduce such distortion, the number of taps should be increased to reduce ripple in both ends of the SRRC filter 70. Therefore, in the related art, in order to design the SRRC filter 70 having the rolloff coefficient r of 0.05, the design should be 100 tap or more to reduce the distortion.

In order to solve the above problems, an object of the present invention is to provide a TDS-OFDM transmitter which reduces the signal distortion caused by the SRRC filter of the TDS-OFDM transmitter and reduces the complexity of implementing the SRRC filter.

1 is a schematic block diagram of a conventional TDS-OFDM transmitter;

2 is a diagram illustrating a spectrum of OFDM symbol data in the frequency domain according to FIG. 1;

3 is a schematic block diagram of a TDS-OFDM transmitter according to the present invention;

4 is a diagram showing a spectrum of OFDM symbol data in the frequency domain according to FIG. 2;

5 is a flowchart illustrating a signal processing method of a TDS-OFDM transmitter according to FIG. 3, and

6 is a diagram comparing signal distortion states by the SRRC filters of FIGS. 1 and 3.

Explanation of symbols on the main parts of the drawings

100: FEC200: serial / parallel converter

300: 3780-IDFT400: Parallel / Serial Conversion

500: GI insertion part 600: PN part

700: 0.01 SRRC filter part 800: RF part

In order to achieve the above object, a TDS OMD transmitter according to an embodiment of the present invention is an inverse Fourier signal processing inversely to N sample data in a time domain by processing a signal such that the frequency interval D between N subcarriers in a frequency domain. A conversion section, a protection section insertion section for inserting a guard section into the N sample data converted from the inverse Fourier transform, a PN section for inserting a PN sequence into the N sample data having the guard section inserted therein, and a PN sequence, a guard section and N And a filter section for filtering the waveform of the OMD signal having two pieces of sample data corresponding to the predetermined rolloff coefficient r. here, , X is the bandwidth occupied by the N subcarriers.

Preferably, the inverse Fourier transform unit is subjected to a signal processing so that the frequency interval is D <2KHz to inverse Fourier transform into N sample data in the time domain, and the roll-off coefficient of the filter unit is r> 0.05.

X, which is a bandwidth occupied by the N subcarriers, That is, when the rolloff coefficient r is 0.11 and the bandwidth is 8 MHz, X is 7.182 MHz.

As a result, when N is 3780, the frequency interval is D = 1.9 KHz.

On the other hand, the signal processing method according to the TDS-FM transmitter in accordance with the present invention, the signal processing to the frequency interval D between the N sub-carriers in the frequency domain by performing a Fourier transform into N sample data in the time domain; Inserting a guard interval into the N sample data inversely Fourier transformed; Inserting a PN sequence into the N sample data into which the guard interval is inserted; And filtering the waveform of the OMD signal having the PN sequence, the guard period, and the N sample data corresponding to the predetermined rolloff coefficient r.

Preferably, the inverse Fourier transform step inverts the Fourier transform into N sample data in the time domain by processing a signal such that the frequency interval is D <2KHz, and the filtering step corresponds to a rolloff coefficient having a rolloff coefficient of r> 0.05. It characterized by filtering.

Therefore, by reducing the interval between the subcarriers in the frequency domain to a predetermined frequency, it is possible to reduce the signal distortion occurring at both ends of the SRRC filter to reduce the distortion of data carried by the subcarriers located at both ends.

Hereinafter, with reference to the drawings will be described in detail an embodiment according to the present invention.

3 is a schematic block diagram of a TDS-OFDM transmitter according to the present invention. The TDS-OFDM transmitter includes a forward error corrector (FEC) 100, a serial / parallel conversion unit 200, a 3780-IDFT (Inverse Fast Fourier Transform) 300, and a parallel / serial conversion unit (TDS-OFDM). 400), a GI (Guard Interavl) insertion unit 500, a PN unit 600, a 0.11 SRRC filter unit 700, an RF unit 800, and the like.

The FEC 100 codes the input data bit stream so that the receiver can detect and correct an error by an error detection method set for an OFDM symbol.

The serial / parallel converter 200 converts the error coded serial data into 3780 parallel data and outputs the parallel data. Thereafter, the 3780-IDFT 300 sets 3780 parallel data so that the frequency spacing D of the subcarrier is less than 2 KHz. That is, the interval D between subcarriers is a frequency obtained by dividing X satisfying Equation 1 below by 3780, which is the number of subcarriers.

Here, X is the bandwidth occupied by the subcarrier, Bandwidth is 8MHz, which is a general bandwidth, and r is the rolloff coefficient r of the SRRC filter. For example, in the case of US DTV, the rolloff coefficient r of the SRRC filter is 0.1152. Referring to this, when the rolloff coefficient r of Equation 1 is 0.11, the bandwidth X occupied by the subcarriers is 7.182 MHz, and the interval D between the subcarriers is 1.9 KHz (7.182 MHz / 3780).

Therefore, as shown in FIG. 4, the interval D between 3780 subcarriers in the frequency domain is 1.9 KHz, and thus the frequency band is 3780 × 1.9 KHz = 7.182 MHz. Therefore, a bandwidth of 0.818 MHz is available for a typical 8 MHz bandwidth, and a band larger than a conventional available band of 0.44 MHz can be obtained. That is, an available band of 0.409 MHz is provided on both sides of the frequency band 7.182 MHz occupied by the subcarrier.

As such, the 3780 OFDM symbol data having a D between the subcarriers of 1.9 KHz is modulated by the 3780-IDFT 300 to output 3780 sample data having a sampling rate of 7.182 MHz. The operating frequency of this system is 7.182MHz. The 3780 sample data output in parallel from the 3780-IDFT 300 are converted into serial data by the parallel / serial conversion unit 400 and outputted. The GI (Guard interval) inserting unit 500 outputs the serial data output. A guard interval (GI) is inserted and output in 3780 sample data units, that is, in one OFDM symbol unit. The guard period (GI) is a copy of some sample data at the end of the OFDM symbol composed of 3780 sample data and is inserted at the front of the OFDM symbol. Thereafter, the PN unit 600 inserts a timing synchronization signal and a PN sequence for channel prediction in front of the guard period GI into the signal having the guard interval inserted therein.

A 0.11 Square root raised cosine (SRRC) filter unit 700 is provided to shape the PN sequence into a predetermined waveform for the generated signal, and the OFMD frame into which the PN sequence is inserted is provided by the 0.11 SRRC filter unit 700. Is filtered.

Here, the rolloff coefficient r of the SRRC filter 700 is set to 0.11. As shown in FIG. 6, in the SRRC filter 700 of 50 taps, the signal distortion of the rolloff coefficient r is increased to 0.11 (B) as compared with the case where the rolloff coefficient r is 0.05 (A). can see. Therefore, signal distortion can be reduced in both ends of the SRRC filter 700, thereby reducing distortion of data carried by subcarriers located at both ends. Thereafter, the OFDM signal filtered by the SRRC filter 700 is transmitted to the radio channel through the RF unit 800.

As described above, as the frequency domain reduces the interval D between subcarriers, thereby greatly applying the rolloff coefficient r of the SRRC filter, it is possible to prevent distortion of signals at both ends of the OFDM symbol data and also to prevent both ends of the SRRC filter. This can reduce the complexity of designing very rapidly.

Hereinafter, a signal processing method of a TDS-OFDM transmitter will be described in detail with reference to FIG. 5.

The OFDM symbol data encoded by the FEC 100 is converted into 3780 parallel data by the serial / parallel conversion unit 200 and output. Thereafter, the 3780-IDFT 300 sets 3780 parallel data so that the frequency interval D of the subcarrier is smaller than 2 KHz. The interval D between these subcarriers is a frequency obtained by dividing [Equation 1] by 3780.

For example, in the case of DTV for the US, the interval D between subcarriers is set to 1.9 KHz by Equation 1 with reference to the rolloff coefficient r of the SRRC filter having 0.1152.

As such, the 3780 OFDM symbol data having a D between the subcarriers of 1.9 KHz is modulated by the 3780-IDFT unit 300 and output as a 3780 sample data having a sampling rate of 7.182 MHz. (S10).

The 3780 sample data output in parallel from the 3780-IDFT 300 are converted into serial data by the parallel / serial conversion unit 400 and outputted. The GI (Guard interval) inserting unit 500 outputs the serial data output. A guard interval (GI) is inserted and output in 3780 sample data units, that is, in one OFDM symbol unit (S20). Thereafter, the PN unit 600 inserts a timing synchronization signal and a PN sequence for channel prediction in front of the guard period GI into the signal having the guard interval inserted (S30).

The OFDM signal generated as described above is pulse shaped by a 0.11 square root raised cosine (SRRC) filter unit 700 having a rolloff coefficient r of 0.11 (S40). Therefore, as shown in FIG. 6, when the rolloff coefficient r is 0.11 (B), the signal distortion can be reduced at both ends of the 0.11 SRRC filter unit 700 so that the data carried by the subcarriers positioned at both ends thereof can be reduced. Can reduce distortion. Thereafter, the OFDM signal filtered by the 0.11 SRRC filter unit 700 is transmitted to the wireless channel through the RF unit 800 (S50).

As such, the rolloff coefficient r of the SRRC filter can be largely applied by reducing the interval between subcarriers in the frequency domain. Therefore, it is possible to prevent distortion of signals in both ends of the OFDM symbol data and to reduce the complexity of designing both ends of the SRRC filter very rapidly.

According to the present invention, by reducing the interval between subcarriers in a frequency domain to a predetermined frequency, it is possible to reduce signal distortion occurring at both ends of the SRRC filter, thereby reducing distortion of data carried by the subcarriers located at both ends.

In addition, it is possible to reduce the complexity of designing both ends of the SRRC filter very rapidly.

In the above described and illustrated with respect to the preferred embodiment of the present invention, the present invention is not limited to the specific preferred embodiment described above, without departing from the gist of the invention claimed in the claims in the art Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

Claims (10)

The frequency interval is D for N carriers in the frequency domain, X is an inverse Fourier transform unit which performs inverse Fourier transform to N sample data in a time domain by processing the signal such that the frequency interval becomes D under a condition that N subcarriers occupy a bandwidth, and the N inverted Fourier transforms. A protection section insertion section for inserting a protection section into sample data, a PN section for inserting a PN sequence into the N sample data into which the protection section is inserted, and the PN sequence, the protection section, and the N sample data A TDS-FM transmitter having a filter unit for filtering a waveform of an OMD signal in response to a predetermined rolloff coefficient r, The inverse Fourier transform unit performs a signal processing such that a frequency interval D becomes D <2KHz, and inverse Fourier transforms the N sample data for the time domain. And the filter unit has a rolloff coefficient r of r> 0.05. The method of claim 1, X is calculated by the following equation TDS-PM transmitter: Here, r is a roll off coefficient (r) of the filter part and bandwidth is 8 MHz. The method of claim 1, And a roll-off coefficient (r) of 0.11. The method of claim 2, X is 7.182MHz T-OS transmitter. The method of claim 1, N is characterized in that 3780, The frequency interval, T = OFM transmitter, characterized in that D = 1.9KHz. The frequency interval is D for N carriers in the frequency domain, X is inversely Fourier transformed into N sample data in a time domain by processing the signal such that the frequency interval becomes D under a condition that N is a bandwidth occupied by the N subcarriers, and the inverse Fourier transformed N sample data. Inserting a guard interval, inserting a PN sequence into the N sample data into which the guard interval is inserted, and forming a waveform of an OMD signal having the PN sequence, the guard interval, and the N sample data. A signal processing method of a TDS-FM transmitter having a filtering step corresponding to a predetermined rolloff coefficient r, In the inverse Fourier transform step, the frequency interval D is a signal processing so that D <2KHz to inverse Fourier transform into the N sample data for the time domain, In the filtering step, the roll-off coefficient r is r> 0.05, the signal processing method of the TDS-FM transmitter. The method of claim 6, Wherein X is calculated by the following equation: A signal processing method of a TDS-FM transmitter: Here, r is a roll off coefficient (r) of the filter part and bandwidth is 8 MHz. The method of claim 6, And said roll-off coefficient (r) is 0.11. The method of claim 7, wherein The X is 7.182MHz signal processing method of the TDS-FM transmitter. The method of claim 6, N is characterized in that 3780, The frequency interval, D = 1.9KHz, characterized in that the signal processing method of the TDS-FM transmitter.